Bioconversion of ethylene glycol to glycolic acid for waste polyethylene terephthalate upcycling

Abstract

Enzymatic depolymerization of polyethylene terephthalate (PET) has garnered significant interest as a promising route for closed-loop recycling of polyesters. An integrated bioprocess that further converts ethylene glycol (EG) — a key monomer derived from PET depolymerization — into glycolic acid (GA) not only enables the upcycling of waste PET but also supplies an alternative feedstock for bio-based manufacturing. In this study, we developed a high-performance Escherichia coli GA06 cell factory by employing a systematic engineering strategy: (1) introduction of an efficient catalytic route from EG to GA, (2) construction of a by-product reflux pathway to minimize metabolic losses, and (3) implementation of an NADH cofactor regeneration system to enhance redox balance. The optimized strain GA06 achieved conversion of 876.47 mM EG to 763.70 mM GA with 87.14% molar yield, representing the highest GA titer reported to date by engineered E. coli cells. Remarkably, this biocatalytic system was successfully applied to post-consumer PET enzymatic hydrolysate in a 5 L bioreactor, achieving a GA conversion rate of 91.86% from EG. Compared with direct EG recovery, conversion into GA achieves a 5.18-fold increase in value. Comprehensive material flow analysis (MFA) and techno-economic analysis (TEA) showed that the EG-to-GA conversion route could reduce the total operating cost of PET enzymatic recovery by 17.59%. In summary, this work established a closed-loop biomanufacturing paradigm that enabled the valorization of consumer plastic waste into high-value biomedical polymers, providing a scalable and carbon-neutral solution for sustainable plastic circularity.